With this control customers can select the area of the image they wish and crop the photo. The ratio or  portion of the selected format is always used and is also possible to select a vertical or an horizontal format. From this screen, format or final measures of the photo to be printed can also be decided. 

Cutting a photo reduces the available pixels for the paper format that we have selected. For a quality print you need a resolution of 300dpi in formats up to 30cm and 254 for larger formats.
You can control this resolution as you crop the picture in the bottom right of the image, including a "traffic light" indicating if the resolution is optimal, critical or poor.